Oxygen rich igniter compositions

ABSTRACT

Low (thermal) Vulnerability Ammunition or LOVA is more responsive to the  rmal stimulation of the igniter compositions disclosed herein. The igniter compositions of this invention generate oxygen rich flames upon decomposition. Such igniter compositions comprise nitrocellulose, nitroglycerine, potassium perchlorate and ethyl centralite. An agent comprising one or more titanate salts and/or carbon black may optionally be included in such compositions to the extent of about 0.35% w/w. Such compositions can be extruded and utilized in strand form.

The invention described herein may be manufactured, and licensed by orfor the Government for Governmental purposes without the payment to usof any royalties thereon.

This application is a continuation of application Ser. No. 780,120,filed Sept. 25, 1985.

This invention relates to certain oxygen rich igniter compositions, toprimers made therefrom and to artillery shells and cartridges comprisingsuch primers.

Low Vulnerability Ammunition (LOVA) which is less vulnerable to ignitionby thermal stimulus, especially that introduced by hot metallicparticles has led to the development of low vulnerability propellants.These so-called LOVA propellants are consequently more difficult toignite with standard igniters used in such ammunition. In tankammunition, this property of more difficult ignition exhibits itself inlonger ignition delays, especially at low temperatures together withreduced performance of such ammunition. Thus, any enhanced internal usesafety of such ammunition is counterbalanced by greater vulnerabilityunder enemy fire as a result of a lack of adequate responsiveness.

Ignition of a LOVA propellant charge is complicated by several factors.By design, the material is less vulnerable to thermal ignition thanconventional propellants. If is therefore, more difficult to ignite.Because of lower burning rates, the web and grain size of the propellantare relatively small. This leads to reduced permeability and resistanceto flow of the igniter gases and flamespreading of propellant combustionproducts within the bed.

In ignitability studies of some LOVA propellant formulations which havebeen reported, it appears that the chemical composition of the igniterflame may play an important role in causing the desired ignition. SeeVarney, M. A., Martino, J., and Henry, R., "Ignitability Studies of LOVAPropellants", Proceedings of the 20th JANNAF Combustion Meeting, Oct.1983, CPIA Publ. 383, Vol. I, p. 547. In particular, igniter flamescontaining excess oxygen may tend to be more efficient. It has now beenfound that the igniter compositions of this invention do in fact producethe desired level of performance.

It is not clear at this time whether the improved performance is due toreactions with the decompostion products of the inert binder used in theLOVA propellant or the nitramine contained in the propellant or both. Itmay well be that the inert binder decomposes initially to provide afuel-rich gaseous product which reacts well with the oxidizer richigniter flame. Whatever may be the mechanism by which the ignitercompositions of this invention bring about improved LOVA ammunitionperformance, the fact remains that such improved performance isunexpectedly superior to that obtained by the use of a conventionaligniter composition such as Benite.

Benite is included as the major igniter material in a bayonet-typeelectric primer which is a standard component of LOVA ammunition. Atypical LOVA cartridge contains a granular propellant which is ignitedwith such bayonet-type electric primer. The primer head assemblycontains a bridge wire ignited match which ignites a booster charge ofblack powder. The booster charge ignites the main charge which isBenite. Benite is a physical mixture of nitrocellulose and theconstituents of black powder (also known as gunpowder), namely,potassium nitrate, carbon and sulfur. In a typical twenty-four (24) venthole steel primer, Benite is utilized in the form of twenty-four (24)separate strands, each being 0.22 cm in diameter and each being 25.4 cmor 10 inches long.

Comparable strands are made from the igniter compositions of thisinvention which comprises nitrocellulose in admixture with otheringredients. However, the performance of the strands made from theigniter compositions of this invention have unexpectedly superiorperformance over comparable Benite strands.

According to this invention, an improved composition for igniting lowthermal stimulus vulnerability propellants is provided which comprises amixture of nitrocellulose, nitroglycerine, potassium perchlorate andethyl centralite and an optional amount of from about 0.01% w/w up toabout 0.35% w/w of an agent selected from the-group consisting oftitanate salts, carbon black and mixtures thereof.

The optional agent may, as already noted above consist of either carbonblack alone or carbon black in admixture with one or more titanatesalts. Alternatively, the agent may omit carbon black altogether andconsist purely of one or more titanate salts.

In another aspect of this invention, the improved composition underlyingthe invention is provided in the form an extruded strand.

In yet another aspect of the invention, a cartridge for the propulsionof one or more projectiles therefrom is provided which comprises a bedof low thermal stimulus vulnerability propellant in adjacent location toa primer comprising the composition underlying this invention. In afurther aspect of the invention a cartridge is provided for thepropulsion of one or more projectiles therefrom which comprises a bed oflow thermal stimulus vulnerability propellant in adjacent location to aprimer comprising the extruded strand also underlying this invention.

The following illustrative but non-limiting examples will aid in afurther understanding of the present invention.

Example A

The four ingredients noted below are mixed together in the proportionsshown:

    ______________________________________                                        Ingredient        % w/w                                                       ______________________________________                                        Nitrocellulose    30.8                                                        Nitroglycerine    20.7                                                        Potassium perchlorate                                                                           47.5                                                        Ethyl centralite   1.0                                                        ______________________________________                                    

The resulting mixture is divided into three (3) batches. The first batchis extruded through a 0.075 inch (0.1905 cm) die and cut into 10 inches(25.4 cm) lengths. The second batch is extruded through a 0.22 cm(0.0866 inch) die and cut into 10 inches (25.4 cm) lengths. The thirdbatch is extruded through a 0.110 inch (0.2794 cm) die and cut into 10inches (25.4 cm) lengths.

This demonstrates the ready extrudability of the resulting mixture intoalmost any desired shape.

The ignition effectiveness of the resulting strands is evaluated inaccordance with the procedure described in Varney, M. A., Martino, J.,and Henry, R., "Expanded Ignition Effectiveness Tests of SelectedIgniter Materials with Navy Propellants", Proceedings of the 21st JANNAFCombustion Meeting, Oct. 1984.

The ignition performance of the strands made out of the mixturecomposition described in this example is found to be superior to that ofBenite strands of the same size. The performance of the strands madeaccording to this example is found to be superior to that of comparableBenite strands in that their utilization in tank ammunition results inshorter ignition delays, improved low temperature performance andimproved ballistic efficiency. Likewise, ignitability tests of thestrands made according to this example with a LOVA propellant also showsuperior results as against comparable Benite strands.

Chemical analysis of the decomposition product of the mixturecomposition described in this example shows the presence of 12% (massfraction) oxygen at the flame temperature.

Example B

The four ingredients noted below are mixed together in the proportionsshown:

    ______________________________________                                        Ingredient        % w/w                                                       ______________________________________                                        Nitrocellulose    25.8                                                        Nitroglycerine    15.6                                                        Potassium perchlorate                                                                           57.6                                                        Ethyl centralite   1.0                                                        ______________________________________                                    

The resulting mixture is processed and tested in the same manner asdescribed in Example A above.

Once again, the ignition performance of the strands made out of themixture composition described in this example is found to be superior(in the same respects) to that of Benite strands of the same size.

Chemical analysis of the decomposition product of the mixturecomposition described in this example shows the presence of 19% (massfraction) oxygen at the flame temperature.

Example C

A mixture is prepared which is substantially identical to that describedin Example A except that 0.12% w/w less is employed of all ingredientsexcept ethyl centralite and the balance is made up with 0.36% w/w ofcarbon black.

The resulting mixture has improved propellant processing and combustioncharacteristics as against the mixture of Example A.

Example D

A mixture is prepared which is substantially identical to that describedin Example A except that 0.12% w/w less is employed of all ingredientsexcept ethyl centralite and the balance is made up with 0.36% w/w of atitanate salt.

The resulting mixture has improved propellant processing and combustioncharacteristics as against the mixture of Example A.

Example E

A mixture is prepared which is substantially identical to that describedin Example A except that 0.12% w/w less is employed of all ingredientsexcept ethyl centralite and the balance is made up with 0.36% w/w of amixture of titanate salts.

The resulting mixture has improved propellant processing and combustioncharacteristics as against the mixture of Example A.

Example F

A mixture is prepared which is substantially identical to that describedin Example A except that 0.12% w/w less is employed of all ingredientsexcept ethyl centralite and the balance is made up with 0.36% w/w of amixture which comprises equal quantities of carbon black and of atitanate salt.

The resulting mixture has improved propellant processing and combustioncharacteristics as against the mixture of Example A.

Example G

A mixture is prepared which is substantially identical to that describedin Example A except that 0.12% w/w less is employed of all ingredientsexcept ethyl centralite and the balance is made up with 0.36% w/w of amixture which comprises equal quantities of carbon black and of amixture of titanate salts.

The resulting mixture has improved propellant and combustioncharacterrstics as against the mixture of Example A.

As the above Examples illustrate, variation of the potassium perchloratecomponent of the igniter composition of this invention from 47% w/w to58% w/w results in the presence in the gaseous decomposition product ofsuch igniter composition of free oxygen in range of 12% (mass fraction)to 19% (mass fraction) at the flame temperature.

All variations of the four components noted in Examples A and B withinthe ranges indicated therein may be gainfully utilized. Lower amounts ofpotassium perchlorate may also be gainfully utilized. For any givenapplication, a person of ordinary skill in the art to which the presentinvention pertains (or artisan) will be able to formulate suitableproportions for each one of the respective ingredients without having toresort to undue experimentation. All that such artisan will need to bearin mind is that the decomposition product of the resulting compositionshpuld preferably contain from 10% (mass fraction) to 20% (mass fraction) free oxygen at the flame temperature.

The scope of the present invention is further defined by and should beread in conjunction with the appended claims.

What is claimed is:
 1. An improved oxygen-rich igniter composition for use with low thermal stimulus vulnerability propellants consisting essentially of:a. nitrocellulose between about 25.8% and 30.8%, b. nitroglycerin between about 15.6% and 20.7%, c. potassium perchlorate between about 47.5% and 57.6%, and d. ethyl centralite at about 1.0%,all percentages being by weight based on the weight of the igniter composition.
 2. The igniter composition of claim 1 including about 0.35% by weight of an agent selected from the group consisting of titanate salts, carbon black, and mixtures thereof.
 3. An improved oxygen-rich igniter composition for use with low thermal stimulus vulnerability propellants consisting essentially of:a. nitrocellulose at about 30.8%, b. nitroglycerin at about 20.7%, c. potassium perchlorate at about 47.5%, and d. ethyl contralite at about 1%,all percentages being by weight based on the weight of the igniter composition.
 4. The igniter composition of claim 3 including about 0.35% by weight of an agent selected from the group consisting of titanate salts, carbon black, and mixtures thereof.
 5. An improved oxygen-rich igniter composition for use with low thermal stimulus vulnerability propellants consisting essentially of:a. nitrocellulose at about 25.8%, b. nitroglycerin at about 15.6%, c. potassium perchlorate at about 57.6%, and d. ethyl centralite at about 1.%,all percentages being by weight based on the weight of the igniter composition.
 6. The igniter composition of claim 5 including about 0.35% by weight of an agent selected from the group consisting of titanate salts, carbon black, and mixtures thereof. 